Notes on LAH Reduction of Nitrostyrenes

by Beagle


LAH reductions may be quenched in several ways. Sometimes ethyl acetate is used, because hydrogen is not evolved, lowering danger of fire/explosion. This method should not be used with amine products, however, because of side reactions. Another method often used is to simply add H2O, ice chips, or wet solvent till bubbling ceases. The problem with this method is that if too much H2O is added, the resulting inorganic salts become gel-like, causing problems in filtration and washing. Only a slight XS amt of H2O is necessary to cause problems. When the proper amount of H2O is used, the salts form a granular consistency, which is easily filtered. A good solution to this problem is to add n mL of H2O, n mL of 15% NaOH, then 3n mL of H2O for every n g. of LAH used.

A properly quenched rxn can make the difference between an 80% yield and a 95% yield, so I hope this may be of use to someone.

Reference: J. Chem. Soc. Vol 107, p407-10 (1915)